Stepped flow-line optics (SFL) were first developed at the turn of the century [Refs. 1-3] and rapidly found applications in the design of backlights [Refs. 4, 5], optics for combining light sources or efficiently distributing light to several locations [Refs. 6-10].
These optics are characterized by having a lower optic (light distributor) which collects the light from a source and distributes it over a given base surface. The bundle of rays coming from the source and redirected by the light distributor generates a field of flow-lines at the base surface. The design process then continues by following a flow-line, then moving across the flow-lines, then following another flow-line, then moving across them, and so on. Each portion of etendue contained between two consecutive flow lines that are followed by this stepped construction is then controlled by a separate (small) optic. This design method is then characterized by “breaking” the incoming light bundle at the base surface in small portions, each one controlled by a separate (small) optic. This process is such that it is possible to later recombine all these portions, rebuilding the continuity of the entire bundle seamlessly. Examples of optics in which this recombination process occurs and does not occur have been proposed [Ref. 3]. For example, this recombination process does not occur in the optics that combine the light from different light sources onto a single exit aperture. In general, the supporting surface may be flat or curved, open or closed (such as a cylinder) [Refs. 2, 3].
In certain of the configurations disclosed here, the seamless recombination of the bundle always occurs. One component of these devices is then the light distributor (lower optic) which distributes the light from the source on the base surface. The other component is made of many small optics constituting an upper optic (microstructure). Each one of these small optics is a microstructure element.
The optical surfaces of each microstructure element may be close together or far apart, creating different types of configurations. In the first case, the microstructure is very thin compared with the overall thickness of the optic. In the second case, the distance between the surfaces of each microstructure element is much larger than their size, one set of surfaces following the base surface and another set of surfaces following another surface, such as the entrance aperture.
It is the object of embodiments of optical devices proposed in the present specification to enable the design process to introduce many discontinuities in the light bundle, and then to eliminate those discontinuities further down the optic. By contrast, today's aspheric design methods only allow a single discontinuity to be introduced in the surfaces generated [Ref 11].